The invention relates to a valve drive of an internal combustion engine with at least one main camshaft on which at least one cam carrier is provided in fixed rotative relationship to the main camshaft and axially shiftable between two axial positions, wherein at least one valve actuating cam for actuating a gas exchange valve of the combustion engine is assigned to the cam carrier.
Valve drives of the aforementioned type are known from the state of the art. They are used in combustion engines in which the operating cycle of gas exchange valves of individual cylinders of the combustion engine can be influenced for improving the thermodynamic properties. The at least one cam carrier which can also be referred to as cam part, is arranged on the main camshaft in fixed rotative relationship with the camshaft and so as to be axially displaceable. Usually several, i.e., at least two valve-actuating cams are assigned to the cam carrier. Each of these valve-actuating cams has an eccentricity, which serves for actuating one of the gas exchange valves of the combustion engine at a defined rotational angle of the main camshaft. The valve-actuating cams thus co-rotate with the main camshaft so that the respective gas exchange valve of the combustion engine is actuated at least once per revolution of the main camshaft by the assigned valve-actuating cam or its eccentricity. For this purpose, the valve-actuating cam preferably interacts with a cam follower of the gas exchange valve through intimate contact with the cam follower.
Preferably multiple valve-actuating cams are provided which can be assigned to different cam groups. The valve-actuating cams of a cam group differ for example regarding the angular position of their eccentricity or the extent of the eccentricity in radial direction (height) and/or in circumferential direction (length). As a result of the axial displacement of the cam carrier, the cam carrier can be caused to assume at least two axial positions, for example a first and a second axial position. In the first axial position the gas exchange valve is actuated by a first one of the valve-actuating cams and in the second axial position by a second one of the valve-actuating cams, which are assigned to the same cam group. Displacement of the cam carrier thus allows in particular selecting the opening time point, the opening duration and/or the lift of the gas exchange valve, in particular in dependence on an operating state of the combustion engine.
The shifting or displacement of the cam carrier in axial direction occurs by means of an actuating device, which includes a shift gate assigned to the cam carrier and a positionally fixed actuator, which is usually fastened on a cylinder head of the combustion engine. The actuator has for example an extendable catch, which can be brought into engagement with an in particular helical or spiral-shaped sliding track of the shift gate. The sliding track is provided on the shift gate, which is assigned to the cam carrier. The shift gate is for example situated on the cam carrier or is at least operably connected with the cam carrier for effecting the axial shifting. The sliding track is preferably constructed as a radial groove, which traverses the circumference of the shift gate, i.e., it is formed in the shift gate so as to have an open rim. The shift gate has thus at least one sliding track into which the catch of the actuator can be introduced for shifting the cam carrier.